The invention generally relates to scan antennas and is specifically directed to a low profile scan antenna mounting system which has an effective gimbal axis in front of the antenna aperture.
Antenna mounting systems typically utilize X-Y type pedestals having azimuth and elevation rotational axes. For example, such antenna pedestals include structures which utilize a yoke supported on a rotatable mount. More specifically, some supporting systems for antennas utilize an arcuate yoke mounted to rotate about a first gimbal axis which is perpendicular to a plane which passes through the yoke. An inner gimbal assembly is mounted in the yoke to rotate about a second gimbal axis which is orthogonal to the first gimbal axis. The antenna or similar device is mounted to the inner gimbal assembly. Examples of such support structures are shown in U.S. Pat. Nos. 2,654,031; 3,351,946; 3,383,081; 4,238,802; and 4,282,529.
Other antenna mounting structures utilize relatively complex arrangements to reduce the swept volume of the antenna for operation in a limited amount of space, such as in an aircraft. For example, U.S. Pat. No. 3,860,930 discloses an antenna scan apparatus for use in an aircraft nosecone which includes an epicyclic gear train to rotate the antenna in a swept volume which is generally triangular. As another example, U.S. Pat. No. 4,225,868 discloses an X-Y antenna pedestal which utilizes multi-hinge points to achieve a lower profile.
Typical aircraft antenna mounting structures such as the above are either complex or bulky or both, and have required relatively large radomes and fuselage openings to accommodate wide angle scanning. The above described antenna characteristics have resulted in problems when applying the antennas to use in modern aircraft. Considerations such as the aerodynamic requirements, space limitations, and operational environment requirements of modern aircraft require radome structures which follow the contour of the aircraft, which have minimum fuselage openings for the antenna aperture, and require a compact or low profile antenna structure. Such requirements also impose problems concerning the scan angles that can be achieved with prior types of antenna mounts. For example, a typical X-Y antenna pedestal having a gimbal axis which is below or behind the radiating aperture requires an opening for the antenna aperture which is considerably larger than the antenna reflector size to achieve an antenna scan over a 140 degree cone.
In addition to the above described antenna types, there are electrical scan antennas including phased array systems. However, such systems occupy a substantial volume due to bulky integral equipment such as power dividers, phase shifters, waveguide "plumbing", amplifiers, control lines, etc. Also included are hybrid array scanning antenna systems, however these systems are also relatively large and complex and requires numerous mechanical components including lens elements.